PHYSIOLOGY: J. WEB 
117 
tephritic trachyte, or to Lacroix's nephelite-micromonzonite. It is proposed 
to call this particular variety of rock, tautirite, from the valley in which it 
occurs. 
On Tahiti, in the valley of Ururoa on the north coast, there is a variety of 
hauynophyre with microscopic hauynites, analysis, 13, which is chemically 
somewhat like the hauynophyres analyzed and described by Lacroix, and by 
Marshall. The microcrystalline groundmass consists of alkalic feldspar, 
augite and magnetite, with small phenocrysts of haiiynite, augite and very few 
brown hornblendes. A similar hauynophyre occurs sparingly in the valley 
of Faurahi, on the southwest side of Tahiti. Its chemical analysis is no. 12. 
These rocks are scarce on Tahiti; 
On Raiatea the heavy sheet of trachytic lava, which tops the ridge and spurs 
of the northern half of the island, varies somewhat in composition in different 
places. On the second spur west of Mount Tapioi it has numerous phenocrysts 
of feldspar, with fewer of mica and paramorphs of hornblende. The chemical 
analysis, no. 10, shows it is kohalaite, or oligoclase-trachyte. A non-porphy- 
ritic gray lava on Moorea is unusual in appearance for rocks of this region. 
Its chemical analysis, no. 9, shows it is latite, an aphanitic lava phase of mon- 
zonite. The corresponding monzonite occurs as a variety of the syenitic 
rocks in the core of the Tahitian volcano. 
THE LAW CONTROLLING THE QUANTITY AND RATE OF 
REGENERATION 
By Jacques Loeb 
Rockefeller Institute foe Medical Research, New York 
Communicated, March 18, 1918 
1. It is well known that isolated pieces of a plant or a lower animal may re- 
generate into a whole organism again. In order to replace the current vague 
speculations concerning this phenomenon by a scientific theory in the sense of 
the physicist, quantitative experiments are required. The writer has for the 
past two years made such experiments which have led to a remarkably simple 
law controlling the quantity of regeneration in an isolated piece of an organ- 
ism. This law can be expressed as follows: The mass of tissue regenerated 
by an isolated piece of an organism is under equal conditions and in equal time 
in direct proportion to the mass of growth material contained in the sap (or 
blood) of the isolated piece. The experiments on which this law is based 
were carried out on an organism unusually favorable for investigations of this 
kind, namely, the plant Bryophyllum calycinum (known to many laymen as the 
Bermuda 'life plant'). When leaves of this plant are isolated from the stem 
they will regenerate shoots in some or many of their notches. If a piece of 
